Pneumatic Tire

ABSTRACT

In a pneumatic tire, a rubber occupancy ratio in a closed region is in a range of 15% or less. Bead cores have a predetermined wire arrangement structure formed by arranging wire cross sections of bead wires in a cross-sectional view in a tire meridian direction. A tangential contacts an innermost layer in a tire radial direction and the wire cross sections innermost and outermost in a tire lateral direction in the wire arrangement structure from a rim fitting surface side. Contact points of the tangent line are on the innermost and outermost wire cross sections. A gauge is in the tire lateral direction from the midpoint to the rim fitting surface. A rate of change of the gauge between before and after mounting on a rim is in a range from 10% or greater to 60% or less.

TECHNICAL FIELD

The technology relates to a pneumatic tire and particularly relates to a pneumatic tire that can improve rim fittability of the tire while a weight of the tire is reduced.

BACKGROUND ART

In recent years, for weight reduction of a tire, weight reduction of bead portions has been advanced. As a conventional pneumatic tire that addresses weight reduction, a technology described in Japan Unexamined Patent Application No. 2008-149778 has been known in which bead fillers are omitted to reduce a weight of the tire.

However, in the known pneumatic tire described above, deterioration of rim fittability of the tire due to the omission of the bead fillers is a concern.

SUMMARY

The technology provides a pneumatic tire that can improve rim fittability of the tire while a weight of the tire is reduced.

A pneumatic tire according to an embodiment of the technology includes bead cores, a carcass layer, and a rim cushion rubber. The bead cores are formed by annularly and multiply winding one or a plurality of bead wires. The carcass layer is formed of a carcass ply of a single layer or a plurality of layers. The carcass layer is turned back so as to wrap the bead cores and extended between the bead cores. The rim cushion rubber is disposed along a turned back portion of the carcass layer to constitute a rim fitting surface of a bead portion. The turned back portion of the carcass layer contacts a body portion of the carcass layer in a cross-sectional view in a tire meridian direction to form a closed region surrounding the bead cores. A rubber occupancy ratio in the closed region is in a range of 15% or less. The bead cores have a predetermined wire arrangement structure formed by arranging wire cross sections of the bead wires in the cross-sectional view in the tire meridian direction. A tangential line L1, contact points C1, C2, a midpoint Cm of the contact points C1, C2 and a gauge Gm are defined. The tangential line L1 contacts an innermost layer in a tire radial direction and the wire cross sections innermost and outermost in a tire lateral direction in the wire arrangement structure from the rim fitting surface side. The contact points C1, C2 of the tangent line L1 are on the wire cross sections on the innermost and the outermost. The gauge Gm is in the tire lateral direction from the midpoint Cm to the rim fitting surface. A rate of change ΔGm of the gauge Gm between before and after mounting on a rim is in a range from 10% or greater to 60% or less.

In the pneumatic tire according to an embodiment of the technology, (1) the rubber occupancy ratio in the closed region surrounded by the body portion and the turned back portion of the carcass layer, that is, a rubber volume around the bead cores, is set to be considerably low. Thus, since bead fillers can be omitted, this is advantageous in that a weight of the tire can be reduced. Additionally, (2) there is an advantage that the rate of change ΔGm of the rim fitting portion of the bead portion is made appropriate. That is, the lower limit ensures rim fitting pressure and ensures rim fittability of the tire. Additionally, the upper limit suppresses deterioration of workability of mounting of the tire on the rim due to excessive rim fitting pressure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view in a tire meridian direction illustrating a pneumatic tire according to an embodiment of the technology.

FIG. 2 is a cross-sectional view illustrating a bead portion of the pneumatic tire illustrated in FIG. 1.

FIG. 3 is an enlarged view illustrating a rim fitting portion of the bead portion illustrated in FIG. 2.

FIG. 4 is an explanatory diagram illustrating a wire arrangement structure of bead cores illustrated in FIG. 3.

FIG. 5 is an explanatory diagram illustrating the rim fitting portion of the bead portion in a state where the tire is mounted on a rim.

FIG. 6 is an explanatory diagram illustrating the rim fitting portion illustrated in FIG. 3.

FIG. 7 is an explanatory diagram illustrating the rim fitting portion illustrated in FIG. 3.

FIG. 8 is an explanatory diagram illustrating a modified example of the bead cores illustrated in FIG. 4.

FIG. 9 is an explanatory diagram illustrating a modified example of the bead cores illustrated in FIG. 4.

FIG. 10 is an explanatory diagram illustrating a modified example of the bead cores illustrated in FIG. 4.

FIG. 11 is an explanatory diagram illustrating a modified example of the bead cores illustrated in FIG. 4.

FIG. 12 is an explanatory diagram illustrating a modified example of the bead cores illustrated in FIG. 4.

FIG. 13 is an enlarged view illustrating a tire side portion of the pneumatic tire illustrated in FIG. 1.

FIGS. 14A-14C include a table showing results of performance tests of pneumatic tires according to embodiments of the technology.

FIG. 15 is an explanatory diagram illustrating bead cores of a test tire of Conventional Example.

DETAILED DESCRIPTION

Embodiments of the technology are described in detail below with reference to the drawings. However, the technology is not limited to these embodiments. Moreover, constituents of the embodiments include elements that are substitutable while maintaining consistency with the technology, and obviously substitutable elements. Furthermore, the modified examples described in the embodiments can be combined as desired within the scope apparent to one skilled in the art.

Pneumatic Tire

FIG. 1 is a cross-sectional view in a tire meridian direction illustrating a pneumatic tire according to an embodiment of the technology. The same drawing illustrates a cross-sectional view of a half region in the tire radial direction. Also, the same drawing illustrates a radial tire for a passenger vehicle as an example of a pneumatic tire.

In reference to the same drawing, “cross section in a tire meridian direction” refers to a cross section of the tire taken along a plane that includes the tire rotation axis (not illustrated). Reference sign CL denotes the tire equatorial plane and refers to a plane normal to the tire rotation axis that passes through the center point of the tire in the tire rotation axis direction. “Tire lateral direction” refers to the direction parallel with the tire rotation axis. “Tire radial direction” refers to the direction perpendicular to the tire rotation axis.

A pneumatic tire 1 has an annular structure with the tire rotation axis as its center and includes a pair of bead cores 11, 11, a carcass layer 13, a belt layer 14, a tread rubber 15, a pair of sidewall rubbers 16, 16, a pair of rim cushion rubbers 17, 17, and an innerliner 18 (see FIG. 1).

The pair of bead cores 11, 11 are formed by annularly and multiply winding one or a plurality of bead wires made of steel. The pair of bead cores 11, 11 are embedded in bead portions to constitute cores of the right and left bead portions.

The carcass layer 13 has a single layer structure formed of one carcass ply or a multilayer structure formed by layering a plurality of carcass plies, and extends between the right and left bead cores 11, 11 in a toroidal shape, forming the framework of the tire. Additionally, both end portions of the carcass layer 13 are turned back outwardly in the tire lateral direction so as to wrap around the bead cores 11 and fixed. The carcass ply (plies) of the carcass layer 13 is made by performing a rolling process on a plurality of coating rubber-covered carcass cords made of steel or an organic fiber material (e.g. aramid, nylon, polyester, and rayon). The carcass ply (plies) has a carcass angle (defined as an inclination angle of a longitudinal direction of the carcass cords with respect to the tire circumferential direction), as an absolute value, ranging from 80 degrees or more to 90 degrees or less. Although the configuration of FIG. 1 has the single layer structure in which the carcass layer 13 is formed of the single carcass ply, no such limitation is intended, and the carcass layer 13 may have a multilayer structure formed by layering the plurality of carcass plies.

The belt layer 14 is formed by layering a pair of cross belts 141, 142 a belt cover 143, and a pair of belt edge covers 144, and arranged to be wound around the periphery of the carcass layer 13. The pair of cross belts 141, 142 are made by performing a rolling process on a plurality of coating rubber-covered belt cords made of steel or an organic fiber material. The cross belts 141, 142 have a belt angle, as an absolute value, ranging from 20 degrees or more to 55 degrees or less. Furthermore, the pair of cross belts 141, 142 have belt angles (defined as inclination angles of the longitudinal direction of the belt cords with respect to the tire circumferential direction) of mutually different signs, and the cross belts 141, 142 are layered so that the longitudinal directions of the belt cords intersect with one another (so-called crossply structure). The belt cover 143 and the pair of belt edge covers 144 are made by coating belt cover cords made of steel or an organic fiber material with a coating rubber and have belt angles, as an absolute value, from 0 degrees or more to 10 degrees or less. Further, the belt cover 143 and the pair of belt edge covers 144 are, for example, a strip material formed by coating one or a plurality of belt cover cords with a coating rubber and winding the strip material spirally around the outer circumferential surfaces of the cross belts 141, 142 multiple times in the tire circumferential direction.

The tread rubber 15 is disposed outward of the carcass layer 13 and the belt layer 14 in the tire radial direction and constitutes a tread portion of the tire. The pair of sidewall rubbers 16, 16 are disposed outward of the carcass layer 13 in the tire lateral direction and constitute right and left sidewall portions. The pair of respective rim cushion rubbers 17, 17 are disposed inward of the right and left bead cores 11, 11 and the turned back portions of the carcass layer 13 in the tire radial direction to constitute rim fitting surfaces of the bead portions.

The innerliner 18 is an air penetration preventing layer that is disposed on the tire cavity surface and covers the carcass layer 13. The innerliner 18 also suppresses oxidation caused by exposure of the carcass layer 13 and prevents air inside the tire from leaking. In addition, the innerliner 18 is constituted by, for example, a rubber composition with butyl rubber as a main component, thermoplastic resin, thermoplastic elastomer composition made by blending an elastomer component with a thermoplastic resin, and the like. The innerliner 18 is adhered to the carcass layer 13 via a tie rubber (not illustrated).

Bead Filler-Less Structure

FIG. 2 is a cross-sectional view illustrating the bead portion of the pneumatic tire illustrated in FIG. 1. The same drawing illustrates a cross-sectional view in the tire meridian direction of the bead portion in a state before mounting of the tire on a rim.

As illustrated in FIG. 2, the carcass layer 13 is turned back outwardly in the tire lateral direction so as to wrap around the bead cores 11 and fixed. At this time, a closed region X surrounding the bead cores 11 is formed by contact of a turned back portion 132 of the carcass layer 13 with a body portion 131. Also, the closed region X continuous across the entire circumference of the tire forms an annular closed space surrounding the bead cores 11.

The closed region X is defined as a region surrounded by the carcass ply of the carcass layer 13 in a cross-sectional view in the tire meridian direction. Specifically, the area surrounded by the surface of the coat rubber of the carcass ply is defined as the closed region X.

Also, in the configuration of FIG. 2, the carcass layer 13 is formed of the single-layer carcass ply, and the closed region X is formed by self-contact of the carcass ply. On the other hand, in a configuration in which the carcass layer 13 is formed of the plurality of layered carcass plies (not illustrated), the closed region X can be formed by mutual contact of the different carcass plies. For example, the following configuration (not illustrated) is assumed. The carcass layer 13 has a two-layer structure formed by layering first and second carcass plies, a turned back portion of the first carcass ply terminates in the middle of a radial height H1 (see FIG. 2) of the bead cores 11 without in contact with the body portion, and a turned back portion of the second carcass ply extends to radially outward of the bead cores 11 and is in contact with the body portion of the first carcass ply.

At this time, a rubber occupancy ratio in the closed region X is preferably in the range of 15% or less, more preferably in the range of 10% or less, and further preferably in the range of 5% or less. Accordingly, the rubber occupancy ratio in the closed region X surrounded by the body portion 131 and the turned back portion 132 of the carcass layer 13, that is, a rubber volume around the bead cores 11, is set to be considerably low. Thus, a purpose of reducing the weight of the tire brought by omission of bead fillers is achieved. Note that the lower limit of the rubber occupancy ratio is not particularly limited but is preferably 0.1% or greater. Thus, an amount of insulation rubber of the bead cores 11 is properly ensured.

The rubber occupancy ratio is calculated as a proportion (%) of a cross-sectional area of the rubber materials in the closed region X to the overall cross-sectional area of the closed region X in the cross-sectional view in the tire meridian direction.

For example, in the configuration of FIG. 2, the turned back portion 132 of the carcass layer 13 is turned back without including a bead filler in the closed region X and in contact with the body portion 131. Also, the carcass ply of the carcass layer 13 is wound up along the outer circumferential surfaces of the bead cores 11. Thus, only constituent members of the bead cores 11 are present in the closed area X. The constituent members of the bead cores 11 include bead wires 111, the insulation rubbers, bead covers, and wrapping threads.

Note that the bead filler is a reinforcing rubber disposed so as to fill the triangular gap between the bead cores, the body portion, and the turned back portion of the carcass layer, and is disposed to increase rigidity of the bead portion. The bead filler generally has a triangular cross section and has a rubber hardness of 65 or greater to 99 or less.

The rubber hardness is measured in accordance with JIS (Japanese Industrial Standard) K 6253.

Additionally, in the above-described configuration in which the bead filler is omitted, as illustrated in FIG. 2, the turned back portion 132 of the carcass layer 13 is preferably in surface contact with the body portion 131 of the carcass layer 13 and fixed. Additionally, a radial height H2 of the contact portion between the body portion 131 and the turned back portion 132 of the carcass layer 13 preferably has a relationship 0.80≤H2/H1≤3.00 to the radial height H1 of the bead cores 11, and more preferably has a relationship 1.20≤H2/H1≤2.50. Thus, the radial height H2 of the self-contact portion of the carcass layer 13 is made appropriate. In other words, the lower limit causes the turned back portion 132 to stably contact the body portion 131, thus improving durability of the bead portion. In addition, the upper limit suppresses an increase in tire weight due to the excessive amount of the turned back portion 132.

The radial height H1 of the bead cores is measured as the maximum height in the tire radial direction from the innermost layer in the wire arrangement structure of the bead cores in the tire radial direction and the inner end in the tire lateral direction of the wire cross section outermost in the tire lateral direction to an outermost later in the tire radial direction and an outer end in the tire radial direction of the wire cross section outermost in the tire lateral direction.

The radial height H2 of the self-contact portion of the carcass layer is measured as the maximum length of the contact portion between the body portion and the turned back portion of the carcass layer in the tire radial direction.

Additionally, as illustrated in FIG. 2, in the configuration described above, an end portion (reference sign is omitted in the drawing) of the turned back portion 132 of the carcass layer 13 preferably contacts the body portion 131 of the carcass layer 13. In such a configuration, stress concentration at the end portion of the turned back portion 132 is reduced compared to a configuration in which the end portion of the turned back portion 132 is spaced apart from the body portion 131 (not illustrated). Accordingly, separation of the peripheral rubber starting from the end portion of the turned back portion 132 is suppressed.

Additionally, an actual length La2 (dimension symbol is omitted in the drawing) of the contact portion between the body portion 131 and the turned back portion 132 of the carcass layer 13 preferably has a relationship 0.30≤La2/La1≤2.00 to a circumferential length La1 (dimension symbol is omitted in the drawing) of the closed region X, and more preferably has a relationship 0.37≤La2/La1≤1.80. Thus, the actual length La2 of the self-contact portion of the carcass layer 13 is made appropriate. That is, the lower limit properly ensures spring characteristics of the carcass layer 13, ensures steering stability on dry road surfaces, and ensures the durability of the bead portion. In addition, the upper limit suppresses an increase in tire weight due to the excessive amount of the turned back portion 132.

The circumferential length La1 of the closed region X is measured as a periphery length of the surface of the carcass ply constituting the boundary line of the closed region X in the cross-sectional view in the tire meridian direction.

The actual length La2 of the contact portion is measured as a periphery length at the self-contact portion between the body portion and the turned back portion of the carcass layer in the cross-sectional view in the tire meridian direction.

Outer Side Reinforcing Rubber

As illustrated in FIG. 2, the pneumatic tire 1 includes an outer side reinforcing rubber 19, in addition to the sidewall rubber 16 and the rim cushion rubber 17 described above.

Each of the sidewall rubbers 16 are disposed outward of the carcass layer 13 in the tire lateral direction and constitute the sidewall portions of the tire as described above. Additionally, the rubber hardness of the sidewall rubber 16 is in the range of from 40 or more to 70 or less. Furthermore, elongation at break of the sidewall rubber 16 is in the range from 400% or greater to 650% or less.

The elongation at break is measured in accordance with the JIS K6251 standard.

The rim cushion rubber 17 is disposed inward of the bead cores 11 and the turned back portion 132 of the carcass layer 13 in the tire radial direction to constitute the rim fitting surface of the bead portion as described above. Additionally, the rubber hardness of the rim cushion rubber 17 is in the range from 50 or greater to 80 or less. Furthermore, the elongation at break of the rim cushion rubber 17 is in the range from 150% or greater to 450% or less.

The outer side reinforcing rubber 19 is disposed to be sandwiched between the turned back portion 132 of the carcass layer 13 and the rim cushion rubber 17 (see FIG. 2). In such a configuration, particularly in the configuration in which the bead filler is omitted described above, the spring characteristics of the bead portion are reinforced by the outer side reinforcing rubber 19, the steering stability on dry road surfaces is ensured, and the durability of the bead portion is improved.

Furthermore, the rubber hardness of the outer side reinforcing rubber 19 is preferably in the range from 65 or greater to 105 or less, and more preferably in the range from 70 or greater to 100 or less. Thus, the above effect of the outer side reinforcing rubber 19 is properly ensured.

Additionally, the rubber hardness of the outer side reinforcing rubber 19 is higher than the rubber hardnesses of the sidewall rubber 16 and the rim cushion rubber 17. Specifically, a difference ΔHs_SW between the rubber hardness of the sidewall rubber 16 and the rubber hardness of the outer side reinforcing rubber 19 is preferably seven or more, and more preferably 12 or more. Additionally, a difference ΔHs_RC between the rubber hardness of the rim cushion rubber 17 and the rubber hardness of the outer side reinforcing rubber 19 is preferably three or more, and more preferably seven or more. Accordingly, the reinforcing effect of the spring characteristics of the bead portion caused by the outer side reinforcing rubber 19 is appropriately exhibited. Note that the lower limit of the difference ΔHs_SW in rubber hardness is subject to restrictions by the lower limit of the rubber hardness of the outer side reinforcing rubber 19 described above.

Furthermore, the elongation at break of the outer side reinforcing rubber 19 is preferably in the range from 50% or greater to 400% or less, and more preferably in the range from 70% or greater to 350% or less.

For example, in the configuration of FIG. 2, the rim cushion rubber 17 extends over completely from a bead toe Bt to a bead base Bb to form the rim fitting surface to a bead sheet 101 of a rim 10. Additionally, the rim cushion rubber 17 extends outward in the tire radial direction from the bead base Bb along the turned back portion 132 of the carcass layer 13 to form a fitting surface to a flange 102 of the rim 10. Additionally, an end portion outward of the rim cushion rubber 17 in the tire radial direction is inserted between the carcass layer 13 and the sidewall rubber 16, and extends outward in the tire radial direction with respect to the end portion of the turned back portion 132 of the carcass layer 13 and the flange 102 of the rim 10. Additionally, the bead portion may include a chafer (not illustrated).

Note that the rim cushion rubber 17 preferably extends to at least a region from a bead heel Bh to a center portion (a midpoint Cm described later) of an innermost layer in the tire radial direction of the bead cores 11. Thus, the durability of the rim fitting portion of the bead portion is properly secured.

Additionally, in the configuration of FIG. 2, the outer side reinforcing rubber 19 has a shape long in the tire radial direction, and is sandwiched between the turned back portion 132 of the carcass layer 13 and the rim cushion rubber 17. Additionally, the end portion inward in the tire radial direction of the outer side reinforcing rubber 19 overlaps with the bead core 11 in the tire radial direction. Additionally, the outer side reinforcing rubber 19 extends outward in the tire radial direction with respect to the end portion of the turned back portion 132 of the carcass layer 13, and is sandwiched between the body portion 131 of the carcass layer 13 and the sidewall rubber 16. Additionally, the outer side reinforcing rubber 19 covers the end portion of the turned back portion 132 of the carcass layer 13 from outward in the tire lateral direction. Additionally, the outer side reinforcing rubber 19 is adjacent to the turned back portion 132 of the carcass layer 13 over the entire contact portion between the body portion 131 and the turned back portion 132 of the carcass layer 13. Thus, the spring characteristics of the bead portion are appropriately reinforced by the outer side reinforcing rubber 19, the steering stability on dry road surfaces is improved, and the durability of the bead portion is improved. Additionally, the rubber hardness of the outer side reinforcing rubber 19 is higher than the rubber hardnesses of the sidewall rubber 16 and the rim cushion rubber 17. Accordingly, a distribution of the rubber hardness at or near the end portion of the turned back portion 132 of the carcass layer 13 decreases from the end portion of the carcass layer 13 toward the surface of the tire side portion. Accordingly, stress generated at or near the end portion of the carcass layer 13 is reduced, and separation of a carcass terminal portion is suppressed.

Additionally, a radial height H3 from a measurement point of a tire inner diameter RD to an end portion outward of the outer side reinforcing rubber 19 in the tire radial direction and a tire cross-sectional height SH (see FIG. 1) preferably have a relationship 0.10≤H3/SH≤0.60, and more preferably have a relationship 0.15≤H3/SH≤0.50. Accordingly, the radial height H3 of the outer side reinforcing rubber 19 is made appropriate. In other words, the lower limit appropriately reinforces the spring characteristics of the bead portion by the outer side reinforcing rubber 19, improves the steering stability on dry road surfaces, and improves the durability of the bead portion. In addition, the upper limit suppresses an increase in tire weight due to the excessive amount of the outer side reinforcing rubber 19.

The tire inner diameter RD is equal to a rim diameter of a specified rim.

The radial height H3 is measured when the tire is mounted on the specified rim, inflated to a specified internal pressure, and in an unloaded state. Specifically, the radial height H3 is calculated as a difference between the diameter of the end portion outward of the outer side reinforcing rubber 19 in the tire radial direction and the tire inner diameter RD.

The tire cross-sectional height SH is a distance half of the difference between the tire outer diameter and the rim diameter and measured when the tire is mounted on the specified rim, inflated to the specified internal pressure, and in an unloaded state.

“Specified rim” refers to an “applicable rim” defined by the Japan Automobile Tyre Manufacturers Association Inc. (JATMA), a “Design Rim” defined by the Tire and Rim Association, Inc. (TRA), or a “Measuring Rim” defined by the European Tyre and Rim Technical Organisation (ETRTO). Additionally, “specified internal pressure” refers to a “maximum air pressure” defined by JATMA, to the maximum value in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, and to “INFLATION PRESSURES” defined by ETRTO. Additionally, “specified load” refers to a “maximum load capacity” defined by JATMA, the maximum value in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “LOAD CAPACITY” defined by ETRTO. However, in the case of JATMA, for a passenger vehicle tire, the specified internal pressure is an air pressure of 180 kPa, and the specified load is 88% of the maximum load capacity.

Additionally, a radial height H4 from the end portion of the turned back portion 132 of the carcass layer 13 to the end portion outward of the outer side reinforcing rubber 19 in the tire radial direction preferably has a relationship 0.10≤H4/H2 to the radial height H2 of the contact portion between the body portion 131 and the turned back portion 132 of the carcass layer 13, and more preferably has a relationship 0.30≤H4/H2. Thus, the steering stability on dry road surfaces is improved, and the durability of the bead portion is improved. Note that the upper limit of the ratio H4/H2 is subject to restrictions by the upper limit of the ratio H3/SH described above.

Additionally, an amount of overlap H5 between the outer side reinforcing rubber 19 and the bead core 11 in the tire radial direction preferably has a relationship 0.05≤H5/H1≤1.00 to the radial height H1 of the bead cores 11, and more preferably has a relationship 0.10≤H5/H1≤1.00. In addition, the amount of overlap H5 is preferably in a range of 5.0 mm≤H5. Accordingly, the amount of overlap H5 between the outer side reinforcing rubber 19 and the bead core 11 is made appropriate. In particular, the lower limit ensures the amount of overlap H5, and suppresses separation of the rubber at the inner end portion of the outer side reinforcing rubber 19 in the tire radial direction.

The amount of overlap H5 is measured when the tire is mounted on the specified rim, inflated to the specified internal pressure, and in an unloaded state.

Note that, not limited to the above, the outer side reinforcing rubber 19 may be disposed outward in the tire radial direction with respect to the bead cores 11 (not illustrated).

Additionally, a length T1 of a perpendicular line drawn from the end portion of the turned back portion 132 of the carcass layer 13 to the outer surface of the tire side portion and a thickness T2 of the outer side reinforcing rubber 19 on the perpendicular line preferably have a relationship 0.10≤T2/T1≤0.90, and more preferably have a relationship 0.20≤T2/T1≤0.80. Thus, the thickness T2 of the outer side reinforcing rubber 19 is made appropriate. In other words, the lower limit appropriately reinforces the spring characteristics of the bead portion by the outer side reinforcing rubber 19, improves the steering stability on dry road surfaces, and improves the durability of the bead portion. In addition, the upper limit suppresses an increase in tire weight due to the excessive amount of the outer side reinforcing rubber 19.

In addition, in the configuration in which the outer side reinforcing rubber 19 is provided instead of the bead filler as described above, a value K defined by the following Equation (1) is preferably 0.17≤K, and more preferably 0.20≤K. Accordingly, the function of the outer side reinforcing rubber 19 is properly ensured. In Equation (1), W denotes a tire nominal width (mm), I denotes a tire nominal inner diameter (inch), and B denotes a total cross-sectional area of bead wires in bead cores (mm²).

$\begin{matrix} {K = \frac{W^{\frac{4}{3}} \times I^{\frac{2}{3}}}{100 \times B^{2}}} & {{Equation}\mspace{14mu} (1)} \end{matrix}$

Rate of Change of Rim Fitting Portion

In the configuration in which bead fillers are omitted as described above, the rigidity of the bead portions is reduced, and the rim fitting pressure of the bead portions tends to decrease. For the reason, in the configuration of FIG. 2, the bead core 11 has the following configuration to ensure the rim fittability of the tire.

FIG. 3 is an enlarged view illustrating the rim fitting portion of the bead portion illustrated in FIG. 2. FIG. 4 is an explanatory diagram illustrating the wire arrangement structure of the bead cores illustrated in FIG. 3. FIG. 5 is an explanatory diagram illustrating the rim fitting portion of the bead portion in a state where the tire is mounted on the rim. In these drawings, FIG. 3 illustrates the rim fitting portion in the state before mounting on the rim, and FIG. 5 illustrates the rim fitting portion in a state after mounting on the rim. FIG. 4 illustrates a cross-sectional view of the unvulcanized bead cores 11 in the radial direction when the components are alone.

In FIG. 2, the rim fitting surface of the bead portion includes the bead base Bb, the bead toe Bt, and the bead heel Bh, and has a contour shape uniform in the tire circumferential direction. The bead base Bb is a flat region formed inward of the bead portion in the tire radial direction and constitutes a contact surface to the bead sheet 101 of the rim. The bead toe Bt is a tip of the bead portion having an L shape or a V shape in the cross-sectional view in the tire meridian direction, and located innermost of the rim fitting surface in the tire lateral direction. The bead heel Bh is a bent portion that connects the wall surface of the tire side portion to the bead base Bb.

The state before the tire is mounted on the rim (see FIGS. 2 and 3) is defined as a state when the positions of the right and left bead portions are fixed so as to match measurement points of a rim width and a rim diameter of the specified rim in a state where the tire rotation axis is horizontalized and the tire alone is disposed upright. Such a tire shape is closest to the tire shape in a tire vulcanization mold, that is, a natural tire shape before inflation.

The state after the tire is mounted on the rim (see FIG. 5) is defined as a state when the tire is mounted on the specified rim, inflated to the specified internal pressure, and in an unloaded state. In the state where the tire is mounted on the rim, the rim fitting surfaces of the bead portions fit to the rim 10 of the wheel, thus holding the tire. At this time, the bead base Bb of the rim fitting surface is pressed against the bead sheet 101 of the rim 10 and brought into surface contact. Thus, the fitting portion between the bead portion and the rim 10 is sealed, and air tightness inside the tire is ensured. Additionally, the bead heel Bh is located at a connection portion between the bead sheet 101 and the flange 102, a region outside the bead heel Bh of the rim fitting surface abuts on the flange 102 of the rim 10, and the bead portion is held from outward in the tire lateral direction.

As illustrated in FIG. 4, in the cross-sectional view in the tire meridian direction, the bead cores 11 have the predetermined wire arrangement structure in which the wire cross sections of the bead wires 111 are arranged. The wire arrangement structure will be described later.

Here, in the cross-sectional view in the tire meridian direction in the state before the tire is mounted on the rim (see FIG. 3), a tangent line L1 that contacts the innermost layer in the tire radial direction and the wire cross sections innermost and outermost in the tire lateral direction in the wire arrangement structure of the bead cores 11 from the rim fitting surface side is defined. Contact points C1 and C2 of the tangent line L1 to the respective wire cross sections and the midpoint Cm of the contact points C1 and C2 are defined. Additionally, gauges G1, G2, Gm in the tire radial direction from the contact points C1 and C2 and the midpoint Cm to the rim fitting surface are defined. Specifically, in the cross-sectional view in the tire meridian direction, intersection points P1, P2, and Pm between straight lines passing through the contact points C1, C2 and the midpoint Cm and perpendicular to the tire axial direction and the bead base Bb are each drawn up. Distances between the contact points C1, C2 and the midpoint Cm and the intersection points P1, P2, and Pm are measured as the gauges G1, G2, Gm.

Similarly, gauges G1′, G2′, and a Gm′ of the rim fitting portion in the state after the tire is mounted on the rim (see FIG. 5) are defined.

At this time, rates of change ΔG1, ΔG2, ΔGm of the gauges G1, G2, Gm of the rim fitting portion in the states before and after mounting on the rim are each preferably in the range from 10% or greater to 60% or less, more preferably in the range from 15% or greater to 50% or less, further preferably in the range from 20% or greater to 45% or less, and the most preferably in the range from 25% or greater to 40% or less. Thus, the rates of change ΔG1, ΔG2, ΔGm of the gauges G1, G2, Gm are set to be greater than those of a typical tire structure including bead fillers. Accordingly, the rates of change ΔG1, ΔG2, ΔGm of the rim fitting portion are made appropriate. That is, the lower limit ensures rim fitting pressure and ensures rim fittability of the tire. Additionally, the upper limit suppresses deterioration of workability of mounting of the tire on the rim due to excessive rim fitting pressure.

Using the gauges Gi and Gi′ before and after mounting on the rim at the predetermined measurement points, a rate of change ΔGi is defined as ΔGi=(Gi−Gi′)/Gi×100. For example, using the gauge G1 (see FIG. 3) before mounting on the rim and the gauge G1′ (see FIG. 5) after mounting on the rim, the rate of change ΔG1 is calculated as ΔG1=(G1−G1′)/G1×100.

The rates of change ΔG1, ΔG2, ΔGm of the rim fitting portion described above are achieved by, for example, a configuration of a cushion rubber layer 20 described later (see FIG. 6) and a configuration of a taper angle of the bead base Bb (see FIG. 7).

In addition, the rates of change ΔG1, ΔG2, ΔGm of the rim fitting portion preferably meet the condition of |ΔGm−ΔG2|<|ΔG1−ΔGm|. Accordingly, a difference in rate of change |ΔG1−ΔGm| on the bead toe Bt is set greater than a difference in rate of change |ΔGm−ΔG2| on the bead heel Bh. Specifically, the rates of change ΔG1, ΔG2, ΔGm preferably meet the condition 20%≤|(ΔG1−ΔGm)/(ΔGm−ΔG2)|≤450%, and more preferably meet the condition 30%≤|(ΔG1−ΔGm)/(ΔGm−ΔG2)|≤300%. Thus, the relationship between the rates of change ΔG1, ΔG2, ΔGm of the rim fitting portion is made appropriate. That is, the lower limit improves the rim fittability of the tire. Additionally, the upper limit improves workability of mounting of the tire on the rim.

In addition, the rates of change ΔG1, ΔG2, ΔGm of the gauges G1, G2, Gm of the rim fitting portion preferably have a relationship ΔG2<ΔGm<ΔG1. In other words, the rates of change ΔG1, ΔG2, ΔGm increase toward the bead toe Bt. Thus, the rim fittability of the tire is improved.

Additionally, in the configuration of FIG. 3, the gauge G1, G2, Gm of the rim fitting portion in the state before mounting the tire on the rim have a relationship G2<Gm<G1. In other words, the gauges G1, G2, Gm of the rim fitting portion increase toward the bead toe Bt. Thus, the mutual relationship between the rates of change ΔG1, ΔG2, ΔGm is made appropriate. Additionally, in a passenger vehicle tire, the gauge G1 is preferably in the range G1≤8.0 mm, and more preferably in the range G1≤6.0 mm. Also, the gauges G2 is preferably in the range 1.0 mm≤G2, and more preferably in the range 1.5 mm≤G2. Thus, the rubber volume of the rim fitting portion inward of the bead cores 11 in the radial direction is made appropriate.

Additionally, a width Wc2 (mm) (see FIG. 4) of the innermost layer of the wire arrangement structure of the bead cores 11, the rate of change ΔGm (%) at the midpoint Cm, and the tire inner diameter RD (inch) (see FIG. 2) preferably have a relationship 1.0%·mm/inch≤Wc2×ΔGm/Rd≤5.0%·mm/inch, more preferably have a relationship 2.0%·mm/inch≤Wc2×ΔGm/RD≤40%·mm/inch, and further preferably have a relationship 5.0%·mm/inch≤Wc2×ΔGm/RD≤30%·mm/inch. Thus, the relationship between the width Wc2 of the innermost layer of the bead cores 11 and the rate of change ΔGm is made appropriate. That is, the lower limit ensures the rim fittability of the tire. Additionally, the upper limit improves the workability of mounting of the tire on the rim.

As illustrated in FIG. 4, the width Wc2 of the innermost layer of the wire arrangement structure is measured as the maximum width including the wire cross sections on the innermost side and the outermost side in the tire lateral direction.

In addition, the width Wc2 of the innermost layer of the wire arrangement structure is preferably in the range 3.0 mm≤Wc2≤10.0 mm, and more preferably in the range 4.5 mm≤Wc2≤9.6 mm.

Wire Arrangement Structure of Bead Cores

As illustrated in FIG. 4, the bead cores 11 are formed by annularly and multiply winding the bead wires 111, and have the predetermined wire arrangement configuration in the cross-sectional view in the tire meridian direction. The wire arrangement structure is defined by the arrangement of the wire cross sections of the bead wires 111. Additionally, the wire arrangement structure is formed by a plurality of layers layered in the tire radial direction. These layers are formed of the plurality of wire cross-sections arranged in a row in the tire lateral direction. Moreover, the innermost layer of the wire arrangement structure is substantially parallel to the rim fitting surface of the bead portion and is opposed to the bead sheet 101 of the rim 10 during fitting of the tire on the rim (see FIG. 3).

In a manufacturing process of the bead cores 11, a core molding jig (not illustrated) is used, and one or a plurality of the bead wires 111 are wound around the core molding jig in the predetermined wire arrangement structure to mold the unvulcanized bead cores 11. Then, the molded bead cores 11 are pre-vulcanized before a vulcanization molding step of a green tire. Note that no such limitation is intended, and the pre-vulcanization of the bead cores 11 may be omitted. The unvulcanized bead cores 11 may be incorporated into the green tire, and the vulcanization molding step of the green tire may be performed.

Additionally, the bead wire 111 is formed of a wire strand and an insulation rubber covering the wire strand (not illustrated). Additionally, the wire strand is made of steel. Additionally, the insulation rubber is preferably made of a rubber composition having a Mooney viscosity of 70 M or greater. The Mooney viscosity is calculated in accordance with JIS K6300-1: 2013.

Here, in the configuration of FIG. 2, as described above, the turned back portion 132 of the carcass layer 13 contacts the body portion 131 of the carcass layer 13 to form the closed region X surrounding the bead cores 11. In addition, the rubber occupancy ratio in the closed region X is set to be small to achieve the weight reduction of the bead portion. At this time, to increase the durability of the bead portion, a cavity portion in the closed region X is preferably suppressed.

Thus, as illustrated in FIG. 4, the wire arrangement structure of the bead cores 11 has a wedge shape that protrudes toward outward in the tire radial direction. Specifically, a layer in which the number of arrangements of the wire cross sections is the maximum in the wire arrangement structure (in FIG. 4, the second layer from the innermost layer) is defined as the maximum arrangement layer. At this time, the number of layers of the wire cross sections outward in the tire radial direction with respect to the maximum arrangement layer (three layers in FIG. 4) is greater than the number of layers of the wire cross sections inward in the tire radial direction with respect to the maximum arrangement layer (one layer in FIG. 4). Additionally, the number of arrangements of the wire cross sections in each layer outward in the tire radial direction with respect to the maximum arrangement layer monotonically decreases outward in the tire radial direction from the maximum arrangement layer. Furthermore, the number of layers of the wire cross sections is preferably in the range of from four or more to six or less. Additionally, the number of arrangements of the wire cross sections in the maximum arrangement layer in the wire arrangement structure is preferably four or five, and the number of arrangements of the wire cross sections in the outermost layer in the tire radial direction is preferably one or two.

The wire cross sections are preferably arranged in a closest-packed structure in the region outward in the tire radial direction with respect to the maximum arrangement layer. The “closest-packed structure” refers to a state in which centers of the three adjacent wire cross sections are arranged to form a substantially equilateral triangle in the cross-sectional view in the tire meridian direction. In such a closest-packed structure, disposal density of the wire cross sections of the bead cores 11 is increased and a core-collapse resistance of the bead cores 11 is improved compared to a lattice arrangement structure in which the rows of the wire cross sections are orthogonal vertically and horizontally. Note that, in the closest-packed state, it is not necessary for all sets of the adjacent wire cross sections to come into contact with one another, and some sets may be disposed with fine gaps (not illustrated).

In such a configuration, as illustrated in FIG. 3, the body portion 131 and the turned back portion 132 of the carcass layer 13 extend outward in the tire radial direction along the wedge shape of the wire arrangement structure while abutting on the right and left side surfaces in the tire lateral direction of the bead cores 11, and are joined in a Y-shape to come into contact with one another. Thus, a gap between the joining portion of the body portion 131 with the turned back portion 132 of the carcass layer 13 and the top portion (so-called bead top) outward of the bead core 11 in the tire radial direction becomes small, and the durability of the bead portion is improved. In particular, the structure in which bead fillers are omitted described above is preferred in that the rubber occupancy ratio in the closed region X can be reduced. In addition, since the turned back portion 132 can bend at an obtuse angle at the joining position with the body portion 131, the amount of bending of the turned back portion 132 becomes small, and the durability of the bead portion is improved.

The number of arrangements of the wire cross sections in the innermost layer in the tire radial direction in the wire arrangement structure is preferably three or four, and is preferably same as or smaller than the number of arrangements of the wire cross sections in the maximum arrangement layer.

As illustrated in FIG. 4, arrangement angles θ1, θ2 of the wire cross sections at corner portions inward in the tire radial direction and inward and outward in the tire lateral direction in the wire arrangement structure are each defined. At this time, the arrangement angles θ1, θ2 are in the range 80 degrees ≤θ1, and 80 degrees ≤θ2. That is, the arrangement angles θ1, θ2 of the wire cross sections form substantially right angles or obtuse angles. In addition, as illustrated in FIG. 4, the arrangement angles θ1, θ2 of the wire cross sections are preferably in the range 100 degrees ≤θ1≤150 degrees, and 100 degrees≤θ2≤150 degrees. Thus, disruption of the wire arrangement structure during tire vulcanization is suppressed, the rim fittability of the tire is improved, and the durability of the bead portion is improved. Also, when the arrangement angles θ1, θ2 of the wire cross sections have the obtuse angles, the carcass ply can be turned back along the corner portions inward of the bead cores 11 in the tire radial direction. Accordingly, the rubber occupancy ratio in the closed region X can be reduced, and the weight of the bead portion can be reduced further.

The arrangement angles θ1, θ2 are measured as angles formed by lines connecting the centers of the three wire cross-sections constituting the corner portions of the wire arrangement structure.

Additionally, in FIG. 4, a maximum width Wc1 and a maximum height Hc1 of the bead cores 11 and a total cross-sectional area S of the bead wires 111 in the bead cores 11 preferably have a relationship 1.20≤Wc1×Hc1/S≤5.00, more preferably have a relationship 1.50≤Wc1×Hc1/S≤4.50, and further preferably have a relationship 1.80≤Wc1×Hc1/S≤4.00. Thus, the wire arrangement structure of the bead cores 11 is made appropriate. That is, the lower limit ensures the number of arrangements of the wire cross sections, and ensures the rim fittability of the tire. In addition, the upper limit reduces the weight of the bead cores 11.

Note that the total cross-sectional area S of the bead wires does not include the cross-sectional area of the insulation rubbers.

Furthermore, the total cross-sectional area S of the bead wires 111 is preferably in the range 5 mm²≤S≤35 mm², more preferably in the range 6 mm²≤S≤32 mm², and further preferably in the range 7 mm²≤S≤28 mm². Thus, the total cross-sectional area S of the bead wires 111 is made appropriate. Specifically, the lower limit ensures the total cross-sectional area S of the bead wires 111 and ensures the rim fittability of the tire. In addition, the upper limit reduces the weight of the bead cores 11.

In addition, an outer diameter ϕ (see FIG. 4) of the bead wire 111 is preferably in the range 0.8 mm≤ϕ≤1.5 mm, and more preferably in the range 0.9 mm≤ϕ≤1.4 mm, and further preferably in the range 1.0 mm≤ϕ≤1.3 mm. Thus, the outer diameter ϕ of the bead wire 111 is made appropriate. That is, the lower limit ensures the outer diameter ϕ of the bead wire 111, and ensures the rim fittability of the tire. In addition, the upper limit reduces the weight of the bead cores 11.

Additionally, in FIG. 4, a height Hc2 from the tangent line L1 of the innermost layer in the wire arrangement to the maximum width position of the bead cores 11, and the maximum height Hc1 of the bead cores 11 preferably have a relationship 1.10≤(Hc1−Hc2)/Hc2≤2.80, and more preferably have a relationship 1.30≤(Hc1−Hc2)/Hc2≤2.50, and further preferably have a relationship 1.50≤(Hc1−Hc2)/Hc2≤2.30. Thus, the wire arrangement structure of the bead cores 11 is made appropriate.

The maximum height Hc1 of the bead cores is measured as the maximum height of the bead cores from the tangent line L1.

The height Hc2 of the widest position of the bead cores is measured as a distance between the tangent line L1 and an imaginary line connecting the centers of the wire cross sections constituting the maximum arrangement layer. In a configuration in which the wire arrangement structure includes the plurality of maximum arrangement layers, the maximum arrangement layer on the outermost in the tire radial direction is used to measure the height Hc2 of the maximum width position.

For example, in the configuration of FIG. 4, the number of layers of the wire cross sections is five, and the number of arrangements of the wire cross sections is set to 3-4-3-2-1 in the order from the innermost layer in the tire radial direction. Thus, the number of arrangements of the wire cross sections in the maximum arrangement layer is four. Additionally, the number of layers of the wire cross sections outward in the tire radial direction with respect to the maximum arrangement layer is three, and the number of layers of the wire cross sections inward in the tire radial direction with respect to the maximum arrangement layer is one. Accordingly, the maximum arrangement layer is asymmetric in the tire radial direction and disposed so as to be biased inward in the tire radial direction with respect to the center position in the tire radial direction of the wire arrangement structure. The wire arrangement structure has a structure long outward in the tire radial direction from the maximum arrangement layer. Moreover, the number of arrangements of the wire cross sections in each layer decreases one by one outward in the tire radial direction from the maximum arrangement layer. Also, all wire cross-sections are arranged in the closely-packed structure. Thus, both of the arrangement angles θ1, θ2 of the wire cross sections at the left and right corner portions in the tire radial direction of the wire arrangement structure are approximately 135 degrees (specifically, in the range of from 130 degrees to 140 degrees). Moreover, the maximum arrangement layer of the wire cross-sections is not the innermost layer in the tire radial direction. In addition, the number of arrangements of the wire cross sections in each layer increases one by one from the innermost layer to the maximum arrangement layer. This optimizes the wire arrangement structure.

Additionally, in FIG. 3, a distance Hg in the tire radial direction from the end portion outward of the bead cores 11 in the tire radial direction to the contact portion between the body portion 131 and the turned back portion 132 of the carcass layer 13 preferably has a relationship Hg/ϕ≤7.0 to the outer diameter ϕ of the bead wire 111, and more preferably has a relationship Hg/ϕ≤3.0. Thus, the rigidity around the bead cores 11 is improved. Note that the lower limit of the ratio Hg/ϕ is 0≤Hg/ϕ in the case of Hg=0.

Gauges of Rim Fitting Portion

FIG. 6 is an explanatory diagram illustrating the rim fitting portion illustrated in FIG. 3. The same drawing illustrates the rim fitting portion in the state before mounting on the rim. In the same drawing, constituents that are the same as constituents illustrated in FIG. 3 have the same reference signs, and explanations thereof are omitted.

In FIG. 6, as described above, the gauge G2 in the tire radial direction from the contact point C2 between the tangent line L1 of the innermost layer of the wire arrangement and the wire cross section outermost in the tire lateral direction to the rim fitting surface is defined. At this time, the gauge G2 and the outer diameter ϕ (see FIG. 4) of the bead wire 111 preferably have a relationship 1.3≤G2/ϕ≤9.5, and more preferably have a relationship 1.8≤G2/ϕ≤5.5. Thus, the gauge G2 of the rim fitting portion is made appropriate. Specifically, the lower limit ensures the gauge G2 of the rim fitting portion and ensures the rim fittability of the tire. Additionally, the upper limit suppresses deterioration of workability of mounting of the tire on the rim due to the excessive gauge G2 of the rim fitting pressure.

Additionally, in FIG. 6, an intersection point Q between a straight line passing through the contact point C2 of the bead core 11 and parallel to the tire lateral direction and a wall surface outward of the rim fitting portion in the tire lateral direction is defined. Also, a gauge Wh in the tire lateral direction from the contact point C2 of the bead core 11 to the point Q at the rim fitting surface is defined. At this time, the gauge Wh and the outer diameter ϕ (see FIG. 4) of the bead wire 111 preferably have a relationship 2.0≤Wh/ϕ≤15.0, and more preferably have a relationship 2.5≤Wh/ϕ≤10.0. Thus, the gauge Wh of the rim fitting portion is made appropriate. That is, the lower limit ensures the gauge Wh of the rim fitting portion, ensures the rim fittability of the tire, and ensures the durability of the rim fitting portion. Additionally, the upper limit suppresses deterioration of workability of mounting of the tire on the rim due to the excessive gauge Wh of the rim fitting pressure.

Additionally, as illustrated in FIG. 6, the cushion rubber layer 20 is inserted between the innermost layer of the bead cores 11 and the rim cushion rubber 17. The cushion rubber layer 20 is a member having a rubber hardness lower than that of the rim cushion rubber 17, includes, for example, the innerliner 18 and a tie rubber (not illustrated) that bonds the innerliner 18 and the carcass layer 13 together, and does not include the carcass ply. Additionally, the cushion rubber layer 20 may have an integral structure with the innerliner 18 and the tie rubber, or may have a separate structure (not illustrated). Additionally, the cushion rubber layer 20 may be made of a rubber material same as those of the innerliner 18 and the tie rubber described above, or may be made of a different rubber material (not illustrated). The cushion rubber layer 20 traverses a range from the contact point C1 to the midpoint Cm of the bead cores 11 in the tire lateral direction, and preferably a range from the contact point C1 to the contact point C2. In such a configuration, the cushion rubber layer 20 is interposed between the innermost layer of the bead cores 11 and the rim fitting surface of the bead portion. This increases the rates of change ΔG1, ΔG2, ΔGm of the rim fitting portion, thus improving the rim fittability of the tire. Additionally, the contact pressure of the rim fitting surface to the rim 10 is made uniform.

Additionally, the rubber hardness of the cushion rubber layer 20 is preferably lower than the rubber hardness of the rim cushion rubber 17 by five or more and more preferably eight or more. Thus, the effect of increasing the rates of change ΔG1, ΔG2, ΔGm of the rim fitting portion is appropriately obtained.

For example, in the configuration of FIG. 6, in the cross-sectional view in the tire meridian direction, the cushion rubber layer 20 extends outward in the tire lateral direction from the tire cavity surface along the turned back portion 132 of the carcass layer 13 and is interposed between the bead cores 11 and the rim cushion rubber 17. Also, the cushion rubber layer 20 extends up to the outermost contact point C2 beyond the midpoint Cm of the innermost layer of the bead cores 11. Additionally, the end portion outward of the cushion rubber layer 20 in the tire lateral direction terminates inward in the tire radial direction with respect to the tangent line L1 of the bead cores 11. Accordingly, the end portion of the cushion rubber layer 20 does not extend up to the side surface outward of the bead cores 11 in the tire lateral direction. Thus, the rates of change ΔG1, ΔG2, ΔGm between the bead cores 11 and the rim fitting surface (in particular, the bead base Bb) are effectively increased while the rigidity between the bead cores 11 and the flange 102 (see FIG. 2) of the rim 10 is properly ensured. However, no such limitation is intended, and the end portion outward of the cushion rubber layer 20 in the tire lateral direction may extend up to outward in the tire radial direction with respect to the tangent line L1 of the bead cores 11.

Additionally, in FIG. 6, thicknesses Tc1, Tc2 of the cushion rubber layer 20 in between the measurement points C1 and P1; and C2 and P2 of the gauges G1, G2 of the rim fitting portion preferably have a relationship Tc2<Tc1. In other words, the thickness Tc1 of the cushion rubber layer 20 on the bead toe Bt side is preferably thicker than the thickness Tc2 of the cushion rubber layer 20 on the bead heel Bh side. Thus, the rate of change ΔG1 of the rim fitting portion on the bead toe Bt side becomes greater than the rate of change ΔG2 of the rim fitting portion on the bead heel Bh side (ΔG2<ΔG1), and the rim fittability of the tire is improved.

Additionally, as described above, adjusting the relationship of the thicknesses of the cushion rubber layer 20 in between the measurement points C1 and P1; C2 and P2; and Cm and Pm of the gauges G1, G2, Gm of the rim fitting portion allows adjusting the relationship between the rates of change ΔG1, ΔG2, ΔGm of the rim fitting portion.

Additionally, an average value of the thicknesses of the cushion rubber layer 20 in the region in the tire lateral direction from the contact point C1 to the contact point C2 is preferably in the range of from 0.3 mm or more to 3.0 mm or less. Thus, the average thickness of the cushion rubber layer 20 is made appropriate. In other words, the lower limit appropriately obtains the effect of the cushion rubber layer 20 that increases the rates of change ΔG1, ΔG2, ΔGm of the rim fitting portion. Additionally, the upper limit suppresses the decrease in rigidity of the rim fitting portion caused by the excessive amount of the cushion rubber layer 20.

Additionally, in FIG. 6, the gauge G1 of the rim fitting portion on the bead toe Bt side and the thickness Tc1 of the cushion rubber layer 20 preferably have a relationship 0.03≤Tc1/G1≤0.95, and more preferably have a relationship 0.05≤Tc1/G1≤0.85. Thus, the average thickness of the cushion rubber layer 20 is made appropriate. That is, the lower limit properly ensures the effect of the cushion rubber layer 20, and increases the rate of change ΔG1 of the rim fitting portion. Additionally, the upper limit ensures the gauge G1 of the rim cushion rubber 17, and properly ensures the rim fittability of the tire.

Additionally, on the tire cavity portion side, the cushion rubber layer 20 extends outward in the tire radial direction from the measurement point of the height H1 (see FIG. 2) of the bead cores 11 outward in the tire radial direction preferably by 5 mm or greater.

Shape of Rim Fitting Surface

FIG. 7 is an explanatory diagram illustrating the rim fitting portion illustrated in FIG. 3. The same drawing illustrates the rim fitting portion in the state before mounting on the rim. In the same drawing, constituents that are the same as constituents illustrated in FIG. 3 have the same reference signs, and explanations thereof are omitted.

As illustrated in FIG. 7, in the cross-sectional view in the tire meridian direction in the state before mounting on the rim, a tangent line of the rim fitting surface at an intersection point P2 is defined as an extension line L2 of the bead base Bb.

At this time, an inclination angle α of the extension line L2 of the bead base Bb with respect to the tangent line L1 of the bead cores 11 is preferably in the range 3 degrees ≤α15 degrees, and more preferably in the range 6 degrees ≤α≤12 degrees.

Additionally, the inclination angle α (degree) of the extension line L2 of the bead base Bb, the rate of change ΔGm (%) of the rim fitting portion, and a tire nominal width WA (dimensionless) preferably have a relationship 0%·degree≤ΔGm×α/WA≤7%·degree, and more preferably have a relationship 0.5%·degree≤ΔGm×α/WA≤5.0%·degree. Thus, a ratio ΔGm×α/WA indicative of the rim fittability of the tire is made appropriate. In other words, in general, as the tire nominal width WA becomes large, the rim fittability of the tire tends to be low. Additionally, the greater the inclination angle α of the bead base Bb and the rate of change ΔGm of the rim fitting portion, the greater the fitting pressure to the rim, thus improving the rim fittability of the tire. Accordingly, the lower limit increases the ratio ΔGm×α/WA, and improves the rim fittability of the tire. Additionally, the upper limit suppresses deterioration of workability of mounting of the tire on the rim due to excessive fitting pressure to the rim. Note that when the inclination angle α=0 degrees, ΔGm×α/WA=0 is met.

Additionally, as illustrated in FIG. 7, in the cross-sectional view in the tire meridian direction, when the bead base Bb has a shape formed by connecting the two types of linear portions with the mutually different inclination angles (so-called two-stage tapered shape), the extension line L2 of the linear portion on the bead heel Bh side and an extension line L3 of the linear portion on the bead toe Bt side of the bead base Bb of the rim fitting surface are defined.

At this time, the inclination angles α, βof the extension lines L2 and L3 of the bead base Bb with respect to the tangent line L1 of the bead cores 11 preferably have a relationship 0≤β/α≤5.0, and more preferably have a relationship 1.8≤β/α≤4.0. Thus, the two-stage tapered shape of the bead base Bb is made appropriate. In other words, the lower limit appropriately obtains the effect of improving the rim fittability of the tire brought by the two-stage tapered shape. Additionally, the upper limit suppresses the occurrence of vulcanization failure in the bead base Bb.

Additionally, in FIG. 7, the intersection point R of the two types of linear portions of the bead base Bb is defined.

At this time, a distance Lr in the tire lateral direction from the bead toe Bt to the intersection point R and a distance Lm in the tire lateral direction from the bead toe Bt to the midpoint Cm preferably have a relationship 0.50≤Lr/Lm≤4.0, and more preferably have a relationship 0.70≤Lr/Lm≤3.3. Thus, the position of the intersection point R is made appropriate, and the effect of improving the rim fittability of the tire brought by the two-stage tapered shape is appropriately obtained.

For example, in the configuration of FIG. 7, the arrangement angle θ1 (see FIG. 4) of the wire cross sections at the corner portion inward in the tire radial direction and inward in the tire lateral direction of the wire arrangement of the bead cores 11 is in the range of from 130 degrees or more to 140 degrees or less. Additionally, the two types of linear portions of the bead base Bb are connected with a smooth arc that protrudes outward in the tire radial direction. Also, the intersection point R is located between the contact point C1 and the midpoint Cm of the bead cores 11.

In FIG. 7, a distance Dt in the tire radial direction from the contact point C1 of the bead cores 11 to the bead toe Bt and a distance Wt in the tire lateral direction are each defined. At this time, the distances Dt, Wt and the gauge G1 in the tire radial direction from the contact point C1 to the rim fitting surface preferably have a relationship 7 degrees≤arctan {(Dt−G1)/Wt}≤30 degrees, and more preferably have the relationship 9 degrees≤arctan {(Dt−G1)/Wt}≤25 degrees. Thus, a gradient of the rim fitting surface with respect to the tire axial direction from the bead cores 11 to the bead toe Bt is made appropriate. That is, the lower limit ensures the gradient of the rim fitting surface, and ensures the rim fittability of the tire. Additionally, the upper limit suppresses a decrease in workability of mounting of the tire on the rim due to excessive gradient of the rim fitting surface.

The distance Dt from the contact point C1 to the bead toe Bt and the distance Wt are measured in the state before mounting of the tire on the rim.

Modified Examples

FIGS. 8 to 12 are explanatory diagrams illustrating the modified examples of the bead cores illustrated in FIG. 4. These drawings illustrate a cross-sectional view of the unvulcanized bead cores 11 in the radial direction when the components are alone.

In the configuration of FIG. 4, the tangent line L1 to the innermost layer of the bead cores 11 is parallel to the tire lateral direction. Accordingly, the inclination angle X of the tangent line L1 with respect to the tire lateral direction is X=0 degrees.

However, no such limitation is intended, and as illustrated in FIG. 8, the bead cores 11 may be inclined to the tire lateral direction. Specifically, the bead cores 11 may be inclined inward in the tire radial direction on the bead toe Bt (see FIG. 3) side. In such a configuration, the tangent line L1 of the innermost layer of the bead cores 11 approaches the bead base Bb of the rim fitting surface in parallel. At this time, the inclination angle X of the tangent line L1 with respect to the tire lateral direction is preferably in the range from −10 degrees≤X≤30 degrees. Note that the range of the relative inclination angle α of the extension line L2 of the bead base Bb with respect to the tangent line L1 of the bead cores 11 is as described above.

Additionally, in the configuration of FIG. 4, as described above, the number of arrangements of the wire cross sections is set to 3-4-3-2-1 in the order from the innermost layer in the tire radial direction. Thus, the number of layers of the wire cross sections is five, and the number of arrangements of the wire cross sections in the outermost layer in the tire radial direction is one.

In contrast, in the configuration of FIG. 9, the number of layers of the wire cross-sections is four, and the number of arrangements of the wire cross sections is set to 3-4-3-2 in the order from the innermost layer in the tire radial direction. In the configuration illustrated in FIG. 10, the number of layers of the wire cross-sections is six, and the number of arrangements of the wire cross sections is set to 3-4-5-4-3-2 in the order from the innermost layer in the tire radial direction. Thus, the number of layers of the wire cross sections may be four or six. Additionally, the number of arrangements of the wire cross sections of the outermost layer in the tire radial direction may be two. In such cases, the numbers of layers of the wire cross sections outward in the tire radial direction with respect to the maximum arrangement layer (two layers in FIG. 9 and three layers in FIG. 10) are greater than the numbers of layers of the wire cross sections inward in the tire radial direction with respect to the maximum arrangement layer (one layer in FIG. 9 and two layers in FIG. 10). Moreover, the number of arrangements of the wire cross sections in each layer decreases one by one outward in the tire radial direction from the maximum arrangement layer.

Additionally, in the configuration of FIG. 4, the number of arrangements of the wire cross sections in the innermost layer in the tire radial direction is less than the number of arrangements of the wire cross sections in the maximum arrangement layer (the second layer from the innermost layer). Also, all wire cross-sections that constitute the wire arrangement structure are arranged in the closely-packed structure. Thus, both of the arrangement angles θ1, θ2 of the wire cross sections at the corner portions inward in the tire radial direction and inward and outward in the tire lateral direction in the wire arrangement structure are in the range of from 130 degrees or more to 140 degrees or less.

In contrast, in the configuration of FIGS. 11 and 12, the number of layers of the wire cross sections is five, and the number of arrangements of the wire cross sections is set to 4-4-3-2-1 in the order from the innermost layer in the tire radial direction. Thus, the number of arrangements of the wire cross sections in the innermost layer is the same as the number of arrangements of the wire cross sections in the maximum arrangement layer. Additionally, in the configuration of FIG. 11, the arrangement angle θ1 of the wire cross sections at the corner portion inward in the tire radial direction and inward in the tire lateral direction of the wire arrangement structure has an acute angle, and is in the range of from 55 degrees or more to 65 degrees or less. On the other hand, the arrangement angle θ2 of the wire cross sections at the corner portion outward in the tire lateral direction has an obtuse angle and is in the range of from 130 degrees or more to 140 degrees or less. In the configuration illustrated in FIG. 12, both of the arrangement angles θ1, θ2 of the wire cross sections at the left and right corner portions inward in the tire radial direction of the wire arrangement structure have substantially right angles, and are in the range of from 85 degrees or more to 95 degrees or less. In this manner, at least the arrangement angle θ2 of the wire cross sections at the corner portion outward in the tire lateral direction preferably has the substantially right angle or obtuse angle. In the configuration illustrated in FIG. 12, the wire cross sections are arranged in a lattice shape inward from the maximum arrangement layers in the tire radial direction. In this manner, it is sufficient that the wire cross sections be arranged in the closely-packed structure at least in each layer outward from the maximum arrangement layers in the tire radial direction.

Gauge of Tire Side Portion

FIG. 13 is an enlarged view illustrating the tire side portion of the pneumatic tire illustrated in FIG. 1. The same drawing illustrates an enlarged cross-sectional view in the tire meridian direction at a tire maximum width position A.

In FIG. 13, a total thickness K1 of the tire side portion at the tire maximum width position A is preferably in the range 2.5 mm≤K1≤6.5 mm, and more preferably in the range 3.0 mm≤K1≤6.0 mm. Thus, the total thickness K1 of the tire side portion is made appropriate. That is, the lower limit ensures the total thickness K1 of the tire side portion, and ensures a tire rolling resistance. Also, the upper limit ensures the weight reduction of the tire.

The total thickness K1 of the tire side portion is measured as a distance between the tire inner surface and the tire outer surface at the tire maximum width position A in the cross-sectional view in the tire meridian direction.

In addition, a thickness K2 of a sidewall rubber 16 at the tire maximum width position A is preferably in the range 0.3 mm≤K2≤3.0 mm, and more preferably in the range 0.5 mm≤K2≤2.5 mm. Thus, the thickness K2 of the sidewall rubber 16 is made appropriate. That is, the lower limit ensures the thickness K2 of the sidewall rubber 16 and ensures a cut resistance of the tire side portion. Also, the upper limit ensures the weight reduction of the tire.

Effects

As described above, the pneumatic tire 1 includes the bead cores 11, the carcass layer 13, and the rim cushion rubber 17. The bead cores 11 are formed by annularly and multiply winding one or a plurality of the bead wires 111. The carcass layer 13 is formed of the carcass ply of a single layer or a plurality of layers. The carcass layer 13 is turned back so as to wrap the bead cores 11 and extended between the bead cores 11. The rim cushion rubber 17 is disposed along the turned back portion 132 of the carcass layer 13 to constitute the rim fitting surface of the bead portion (see FIGS. 1 and 2). The turned back portion 132 of the carcass layer 13 contacts the body portion 131 of the carcass layer 13 in the cross-sectional view in the tire meridian direction to form the closed region X surrounding the bead cores 11 (see FIG. 2). The rubber occupancy ratio in the closed region X is in the range of 15% or less. The bead cores 11 have the predetermined wire arrangement structure formed by arranging the wire cross sections of the bead wires 111 in the cross-sectional view in the tire meridian direction (see FIG. 4). The tangential line L1, the contact points C1, C2, the midpoint Cm of the contact points C1, C2 and the gauge Gm are defined. The tangential line L1 contacts the innermost layer in the tire radial direction and the wire cross sections innermost and outermost in the tire lateral direction in the wire arrangement structure from the rim fitting surface side. The contact points C1, C2 of the tangent line L1 are on the wire cross sections on the innermost and the outermost. The gauge Gm is in the tire lateral direction from the midpoint Cm to the rim fitting surface (see FIG. 3). At this time, the rate of change ΔGm of the gauge Gm between before and after mounting on the rim is in the range from 10% or greater to 60% or less.

In such a configuration, (1) the rubber occupancy ratio in the closed region X surrounded by the body portion 131 and the turned back portion 132 of the carcass layer 13, that is, the rubber volume around the bead cores 11, is set to be considerably low. Thus, since bead fillers can be omitted, the weight of the tire can be reduced.

Additionally, (2) there is an advantage that the rate of change ΔGm of the rim fitting portion of the bead portion is made appropriate. That is, the lower limit ensures rim fitting pressure and ensures rim fittability of the tire. The effect is particularly beneficial in the structure in which bead fillers are omitted (see FIG. 2). Additionally, the upper limit suppresses deterioration of workability of mounting of the tire on the rim due to excessive rim fitting pressure.

Additionally, in the pneumatic tire 1, when the layer in which the number of arrangements of the wire cross sections is the maximum in the wire arrangement structure is defined as the maximum arrangement layer (in FIG. 4, the second layer from the innermost layer), the number of layers of the wire cross sections outward in the tire radial direction with respect to the maximum arrangement layer (three layers in FIG. 4) is greater than the number of layers of the wire cross sections inward in the tire radial direction with respect to the maximum arrangement layer (one layer in FIG. 4). Additionally, the number of arrangements of the wire cross sections in each layer outward in the tire radial direction with respect to the maximum arrangement layer monotonically decreases outward in the tire radial direction from the maximum arrangement layer. In such a configuration, there is an advantage that a gap between the joining portion of the body portion 131 with the turned back portion 132 of the carcass layer 13 and the top portion (so-called bead top) outward of the bead core 11 in the tire radial direction becomes small, and the durability of the bead portion is improved. In particular, the structure in which bead fillers are omitted described above is preferred in that the rubber occupancy ratio in the closed region X can be reduced. In addition, there is an advantage that, since the turned back portion 132 can bend at an obtuse angle at the joining position with the body portion 131, the amount of bending of the turned back portion 132 becomes small, and the durability of the bead portion is improved.

Additionally, in the pneumatic tire 1, the width Wc2 (see FIG. 4) of the innermost layer of the bead cores 11, the rate of change ΔGm at the midpoint Cm (see FIG. 3), and the tire inner diameter RD (see FIG. 2) have a relationship 1.0%·mm/inch≤Wc2×ΔGm/RD≤50%·mm/inch. Thus, there is an advantage that the relationship between the width Wc2 of the innermost layer of the bead cores 11 and the rate of change ΔGm are made appropriate. That is, the lower limit ensures the rim fittability of the tire. Additionally, the upper limit improves the workability of mounting of the tire on the rim.

Additionally, in the pneumatic tire 1, in the cross-sectional view in the tire meridian direction, when the extension line L2 (see FIG. 7) of the linear portion of the bead base Bb of the rim fitting surface is defined, the inclination angle α of the extension line L2 with respect to the tangent line L1, the rate of change ΔGm, and the tire nominal width WA have a relationship 0%·degree≤ΔGm×α/WA≤7%·degree. This has an advantage that the ratio ΔGm×α/WA indicative of the rim fittability of the tire is made appropriate. That is, the lower limit improves the ratio ΔGm×α/WA increases, and improves the rim fittability of the tire. Additionally, the upper limit suppresses deterioration of workability of mounting of the tire on the rim due to excessive fitting pressure to the rim.

Additionally, in the pneumatic tire 1, in the cross-sectional view in the tire meridian direction, the bead base Bb of the rim fitting surface is formed by connecting the two types of linear portions with the mutually different inclination angles (see FIG. 7). Additionally, the extension line L2 of the linear portion on the bead heel Bh side and the extension line L3 of the linear portion on the bead toe Bt side of the bead base Bb of the rim fitting surface are defined. At this time, the inclination angles α, β of the extension lines L2 and L3 with respect to the tangent line L1 have a relationship 0≤β/α≤5.0. This has an advantage that the two-stage tapered shape of the bead base Bb is made appropriate. In other words, the lower limit appropriately obtains the effect of improving the rim fittability of the tire brought by the two-stage tapered shape. Additionally, the upper limit suppresses the occurrence of vulcanization failure in the bead base Bb.

Additionally, in the pneumatic tire 1, the intersection point R of the two kinds of linear portions of the bead base Bb is defined (see FIG. 7). At this time, the distance Lr in the tire lateral direction from the bead toe Bt to the intersection point R and the distance Lm in the tire lateral direction from the bead toe Bt to the midpoint Cm have a relationship 0.50≤Lr/Lm≤4.0. This is advantageous that the position of the intersection point R is made appropriate, and the effect of improving the rim fittability of the tire brought by the two-stage tapered shape is appropriately obtained.

Additionally, in the pneumatic tire 1, the arrangement angle θ1 of the wire cross sections at the corner portion inward in the tire radial direction and inward in the tire lateral direction of the wire arrangement is in the range 80 degrees≤θ1 (see FIG. 4). Additionally, in the cross-sectional view in the tire meridian direction, the bead base Bb of the rim fitting surface is formed by connecting the two types of linear portions with the mutually different inclination angles (see FIG. 7). Additionally, when the intersection point R of the two types of linear portions of the bead base is defined, the intersection point R is located between the contact point C1 and the midpoint Cm in the tire lateral direction. This has the advantage that the position of the intersection point R of the two-stage tapered shape is made appropriate and the rim fittability of the tire is improved.

Additionally, the pneumatic tire 1 includes the cushion rubber layer (rim cushion rubber 17 in FIG. 2) that has the rubber hardness lower than that of the rim cushion rubber 17 and is inserted between the innermost layer of the bead cores 11 and the rim cushion rubber 17 (see FIG. 2). The configuration is advantageous that the cushion rubber layer interposed between the bead cores 11 and the rim fitting surface increases the rates of change ΔG1, ΔG2, and ΔGm of the rim fitting portion and improves the rim fittability of the tire.

Additionally, in the pneumatic tire 1, the cushion rubber layer (rim cushion rubber 17 in FIG. 2) traverses the range from the contact point C1 to the midpoint Cm of the bead cores 11 in the tire lateral direction (see FIG. 3). This is advantageous that the effect of improving the rim fittability brought by the cushion rubber layer is effectively obtained.

Additionally, the pneumatic tire 1 includes the outer side reinforcing rubber 19 disposed between the turned back portion 132 of the carcass layer 13 and the rim cushion rubber 17 (see FIG. 2). The configuration, particularly the configuration in which bead fillers are omitted described above, is advantageous that the spring characteristics of the bead portion are reinforced by the outer side reinforcing rubber 19 and the steering stability on dry road surfaces is ensured.

Additionally, in the pneumatic tire 1, the radial height H3 (see FIG. 2) from the measurement point of the tire inner diameter RD to the end portion outward of the outer side reinforcing rubber 19 in the tire radial direction and the tire cross-sectional height SH (see FIG. 1) have the relationship 0.10≤H3/SH≤0.60. This has an advantage that the radial height H3 of the outer side reinforcing rubber 19 is made appropriate. In other words, the lower limit appropriately reinforces the spring characteristics of the bead portion by the outer side reinforcing rubber 19, and improves the steering stability on dry road surfaces. In addition, the upper limit suppresses the increase in tire weight due to the excessive amount of the outer side reinforcing rubber 19.

Additionally, in the pneumatic tire 1, the length T1 of the perpendicular line drawn from the end portion of the turned back portion 132 of the carcass layer 13 to the outer surface of the tire side portion and the thickness T2 of the outer side reinforcing rubber 19 on the perpendicular line have the relationship 0.10≤T2/T1≤0.90. This has an advantage that the thickness T2 of the outer side reinforcing rubber 19 is made appropriate. In other words, the lower limit appropriately reinforces the spring characteristics of the bead portion by the outer side reinforcing rubber 19, and improves the steering stability on dry road surfaces. In addition, the upper limit suppresses the increase in tire weight due to the excessive amount of the outer side reinforcing rubber 19.

Additionally, in the pneumatic tire 1, the arrangement angle θ2 of the wire cross sections at the corner portion inward in the tire radial direction and outward in the tire lateral direction of the wire arrangement structure is in the range 80 degrees≤θ2 (see FIG. 4). This has an advantage that disruption of the wire arrangement structure during tire vulcanization is suppressed, and the rim fittability of the tire is improved.

Additionally, in the pneumatic tire 1, the height Hc2 from the tangent line L1 to the maximum width position of the bead cores 11 and the maximum height Hc1 of the bead cores 11 have the relationship 1.10≤(Hc1−Hc2)/Hc2≤2.80 (see FIG. 4). This has an advantage that the wire arrangement structure of the bead cores 11 is made appropriate.

Additionally, in the pneumatic tire 1, the actual length La2 of the contact portion between the body portion 131 and the turned back portion 132 of the carcass layer 13 has the relationship 0.30≤La2/La1≤2.00 with respect to the circumferential length La1 of the closed region X. Thus, the actual length La2 of the self-contact portion of the carcass layer 13 is made appropriate. In other words, this has an advantage that, the lower limit properly ensures the spring characteristics of the carcass layer 13, and ensures the steering stability on dry road surfaces. In addition, the upper limit suppresses an increase in tire weight due to the excessive amount of the turned back portion 132.

EXAMPLE

FIGS. 14A-14C include a table showing results of performance tests of pneumatic tires according to the embodiment of the technology. FIG. 15 is an explanatory diagram illustrating bead cores of a test tire of Conventional Example.

In the performance test, a plurality of types of test tires having a tire size of 205/55R16 were evaluated for (1) tire mass, (2) rim fittability, and (3) steering stability.

(1) The tire mass is calculated as the average value of the masses of five test tires having the same structure. The measurement results are expressed as index values and evaluated with the Conventional Example being assigned as the reference (100). The smaller the values in this evaluation, the lighter the test tires are, which is preferred. Additionally, when the index is 99 or less, it can be said that the weight of the tire is reduced compared to that of the existing tire structure including bead fillers.

(2) In the evaluation for rim fittability, the test tires are mounted on rims having a rim size of 16×6.5 J, and the test tires are inflated to an air pressure of 230 kPa and a load specified by JATMA is given. The test tires were mounted on a Sport Utility Vehicle (SUV) as a test vehicle with an engine displacement of 2000 cc. Then, the test vehicle performs a J-turn on a predetermined traveling path while the air pressures of the test tires are gradually decreased, and the air pressure at the time of air leakage is measured. The measurement results are expressed as index values and evaluated with the Conventional Example being assigned as the reference (100). In this evaluation, larger values are preferable.

(3) In the evaluation for steering stability, the test vehicle is driven at 60 km/h to 100 km/h on a test course of dry road surfaces including a flat circuit. Then the test driver performed a sensory evaluation regarding steering while lane changing and cornering and stability while traveling forward. Results of the evaluation are expressed as index values and evaluated with the Conventional Example being assigned as the reference (100). In this evaluation, larger values are preferable.

The test tires of Examples 1 to 19 achieve the weight reduction of the tires by having the structures of omitting bead fillers (see FIGS. 1 and 2). Additionally, the gauges G1, Gm, and G2 of the rim fitting portion in the state before mounting on the rim have a relationship G2<Gm<Gb1. Additionally, the rubber hardness of the rim cushion rubber 17 is 70. Additionally, the outer side reinforcing rubber 19 is made of the material same as that of the rim cushion rubber 17 and integrated into the rim cushion rubber 17. The tire cross-sectional height SH is 112 mm, and the length T1 of the perpendicular line drawn from the end portion of the turned back portion 132 of the carcass layer 13 to the outer surface of the tire side portion is 7.0 mm.

In the test tire of Conventional Example, in the structure of the test tire of Example 1, the bead cores 11 have the wire arrangement structure illustrated in FIG. 15. In the test tires of Comparative Examples 1 and 2, in the configurations of FIGS. 1 and 2, the amount of the insulation rubbers of the bead cores 11 are increased, and the rubber occupancy ratio in the closed region X is increased.

As shown from the test results, it is seen that the test tires of Examples 1 to 19 can improve the rim fittability and the steering stability of the tire while the weights of the tires are reduced. 

1. A pneumatic tire, comprising: bead cores formed by annularly and multiply winding one or a plurality of bead wires; a carcass layer formed of a carcass ply of a single layer or a plurality of layers, the carcass layer being turned back so as to wrap the bead cores and extended between the bead cores; a rim cushion rubber disposed along a turned back portion of the carcass layer to constitute a rim fitting surface of a bead portion; the turned back portion of the carcass layer contacting a body portion of the carcass layer in a cross-sectional view in a tire meridian direction to form a closed region surrounding the bead cores; a rubber occupancy ratio in the closed region being in a range of 15% or less; the bead cores having a predetermined wire arrangement structure formed by arranging wire cross sections of the bead wires in the cross-sectional view in the tire meridian direction; a tangential line, contact points, a midpoint of the contact points, and a gauge being defined, the tangential line contacting an innermost layer in a tire radial direction and the wire cross sections innermost and outermost in a tire lateral direction in the wire arrangement structure from the rim fitting surface side, the contact points of the tangent line being on the innermost and the outermost wire cross sections, the gauge being in the tire lateral direction from the midpoint to the rim fitting surface; and a rate of change ΔGm of the gauge between before and after mounting on a rim being in a range from 10% or more to 60% or less.
 2. The pneumatic tire according to claim 1, wherein a layer in which a number of arrangements of the wire cross sections is a maximum in the wire arrangement structure is defined as a maximum arrangement layer, a number of layers of the wire cross sections outward in the tire radial direction with respect to the maximum arrangement layer is greater than a number of layers of the wire cross sections inward in the tire radial direction with respect to the maximum arrangement layer, and a number of arrangements of the wire cross sections in each layer outward in the tire radial direction with respect to the maximum arrangement layer monotonically decreases outward in the tire radial direction from the maximum arrangement layer.
 3. The pneumatic tire according to claim 1, wherein a width Wc2 (mm) of the innermost layer of the bead cores, the rate of change ΔGm (%) at the midpoint, and a tire inner diameter RD (inch) have a relationship 1.0%·mm/inch≤Wc2×ΔGm/RD≤50%·mm/inch.
 4. The pneumatic tire according to claim 1, wherein in the cross-sectional view in the tire meridian direction, an extension line L2 of a linear portion of a bead base of the rim fitting surface is defined, and an inclination angle α (degree) of the extension line L2 with respect to the tangent line L1, the rate of change ΔGm (%), and a tire nominal width WA (dimensionless) have a relationship 0%·degree≤ΔGm×α/WA≤7%·degree.
 5. The pneumatic tire according to claim 1, wherein in the cross-sectional view in the tire meridian direction, a bead base of the rim fitting surface is formed by connecting two types of linear portions with mutually different inclination angles, a first extension line of the linear portion on a bead heel side and a second extension line of the linear portion on a bead toe side of the bead base of the rim fitting surface are defined, and inclination angles α, β of the first and second extension lines with respect to the tangent line have a relationship 0≤β/α≤5.0.
 6. The pneumatic tire according to claim 1, wherein in the cross-sectional view in the tire meridian direction, a bead base of the rim fitting surface is formed by connecting two types of linear portions with mutually different inclination angles, an intersection point of the two types of the linear portions of the bead base is defined, and a distance Lr in the tire lateral direction from a bead toe to the intersection point and a distance Lm in the tire lateral direction from the bead toe to the midpoint have a relationship 0.50≤Lr/Lm≤4.0.
 7. The pneumatic tire according to claim 1, wherein an arrangement angle θ1 of the wire cross sections at a corner portion inward in the tire radial direction and inward in the tire lateral direction of the wire arrangement is in a range 80 degrees≤θ1, in the cross-sectional view in the tire meridian direction, a bead base of the rim fitting surface is formed by connecting two types of linear portions with mutually different inclination angles, an intersection point of the two types of the linear portions of the bead base is defined, and the intersection point is located between one of the contact points and the midpoint in the tire lateral direction.
 8. The pneumatic tire according to claim 1, comprising a cushion rubber layer that has a rubber hardness lower than a rubber hardness of the rim cushion rubber, the cushion rubber layer being inserted between the innermost layer of the bead cores and the rim cushion rubber.
 9. The pneumatic tire according to claim 8, wherein the cushion rubber layer traverses a range from the one of the contact points to the midpoint of the bead cores in the tire lateral direction.
 10. The pneumatic tire according to claim 1, comprising an outer side reinforcing rubber that has a rubber hardness higher than a rubber hardness of the rim cushion rubber, the outer side reinforcing rubber being disposed between the turned back portion of the carcass layer and the rim cushion rubber.
 11. The pneumatic tire according to claim 10, wherein a radial height H3 from a measurement point of the tire inner diameter to an end portion outward of the outer side reinforcing rubber in the tire radial direction and a tire cross-sectional height SH have a relationship 0.10≤H3/SH≤0.60.
 12. The pneumatic tire according to claim 10, wherein a length T1 of a perpendicular line drawn from an end portion of the turned back portion of the carcass layer to an outer surface of a tire side portion and a thickness T2 of the outer side reinforcing rubber on the perpendicular line have a relationship 0.10≤T2/T1≤0.90.
 13. The pneumatic tire according to claim 1, wherein an arrangement angle θ2 of the wire cross sections at a corner portion inward in the tire radial direction and outward in the tire lateral direction of the wire arrangement structure is in a range 80 degrees≤θ2.
 14. The pneumatic tire according to claim 1, wherein a height Hc2 from the tangent line to a maximum width position of the bead cores and a maximum height Hc1 of the bead cores have a relationship 1.10≤(Hc1−Hc2)/Hc2≤2.80.
 15. The pneumatic tire according to claim 1, wherein an actual length La2 of a contact portion between the body portion and the turned back portion of the carcass layer has a relationship 0.30≤La2/La1≤2.00 with respect to a circumferential length La1 of the closed region. 